1. Field of the Invention
This invention relates to pad printing and, in particular, to a pad printing system and apparatus for the printing of long images with a sealed ink cup. Even more particularly, the invention relates to an apparatus for pad printing in which the image printed has a length greater than the diameter of the ink cup being used.
2. Description of the Prior Art
The so-called "pad printing," of substrates with an image, in particular those with irregular surfaces, has long been known. In earlier days, at least in some forms of pad printing, the ink was contained in an ink tray which was exposed to the atmosphere. As the ink is solvent based, the solvent or thinner would evaporate, and over time the viscosity of the ink would increase.
In more recent years, the source of ink in pad printing systems for the printing of an image is a reservoir member having the shape of a cup turned upside down. Illustrative of such cups are those disclosed in U.S. Pat. Nos. 5,003,872 and 5,237,922 and the cup disclosed in European Patent Application No. 93201027.5. Such an ink cup, in general, is passed over a printing plate or member having a top planar surface in which a pattern or image is provided, e.g., a line of print. As the cup passes or travels over the pattern in the printing plate, the pattern is flooded with ink. At the same time that the pattern is flooded with ink, at least in some cases, a rim or lip of the ink cup acts as a doctor blade and wipes off any excess ink from the image pattern surface, leaving ink only in the grooves forming the pattern. The ink pattern is then, in general, transferred to a flexible silicone pad or transfer member placed in pressure contact with the image. The transfer pad is then removed from contact with the printing plate and placed in pressure contact with the surface to be printed, e.g., the surface of a catheter in the case of line printing or the surface of a golf ball in the case of logo printing, and the image is thus transferred to that surface. Meanwhile, the image on the printing plate is again inked. The pad is removed from contact with the surface just printed and returns to its home position for placement in contact again with the inked image on the printing plate. Thus, the image is transferred or pad printed onto the second of the items to be printed. This cycle continues until all the items to be printed with the image have been printed.
In pad printing systems wherein a sealed ink cup was used prior to the invention disclosed herein, the ink cup generally moves across the image to be printed, i.e., in a direction perpendicular to the length of the image. The transfer pad travels in the same direction. Nevertheless, in some pad printing systems, the ink cup is held stationary and the printing plate is moved in an in and out manner relative to the ink cup. Regardless of which system is used, however, the transfer pad moves in an up and down manner and in the same in and out direction as earlier disclosed. In such pad printing systems, however, the length or width of an image that can be printed onto a substrate is somewhat limited. This, of course, is due to the fact that the image size is limited by the diameter of the ink cup being used. The image to be flooded with ink can be of no greater length than such a diameter; otherwise a part of the image will not be inked.
In general, with present pad printing systems, the greater the length or width of image to be printed, the larger must be the diameter of the ink cup used. Thus, theoretically, almost any length image could be printed provided the ink cup diameter is large enough. Nevertheless, providing ever larger diameter ink cups for printing longer, narrow images does not offer a practical solution for a number of reasons. With a round ink cup, the stroke of the ink cup must be at least twice the diameter of the cup. This being so, the use of larger diameter ink cups requires larger more expensive printing apparatus including larger printing plates. Moreover, larger diameter ink cups and printing plates are not only more expensive, they are also difficult to make. Larger pneumatic and other operating components are required with larger printing apparatus. A larger diameter cup not only requires greater ink consumption but results in wasted ink. And, a larger diameter ink cup requires a larger plate size resulting in much wasted material. None of this is desirable, however, as such larger apparatus will require a greater amount of floor space than may be available or desired to give up for such a purpose. Moreover, also of concern, are safety considerations, as well as the difficulty and inconvenience experienced by an operator in loading the printer for use.
Thus, there is a real need for pad printing apparatus wherein an image can be printed with a sealed ink cup of greater length than can now be printed. Moreover, there is a need for pad printing apparatus that can print images of greater length than the diameter of the ink cup, yet be no larger in size than pad printing apparatus now used.